I. Field of the Invention
This invention relates generally to flow circuit valve position indicators, and more particularly to a modular valve position indicator compatible with international standards, and interfaces with a valve, actuator and other auxiliary equipment. A drum having color coded indicia thereon, rotates through a window defined by other members of the modular indicator in response to the rotation of the valve.
II. Discussion of the Related Art
Operating personnel in many industrial and laboratory settings must know, at a glance, whether a fluid-flow control valve is in an open (fluid passing) or closed (fluid blocking) disposition. A commercially available position indicator, a product of Keystone Controls, Inc., of Houston, Tex. provides an indicator that is associated with the valve actuator by a magnetic lobe. The valve position is indicated by green and red LED's. The position indicator comprises one housing and a drum associated with the housing. Many devices have been devised for providing such an indication. In this regard, reference is made to U.S. Pat. Nos. 4,494,565; 4,494,566; 5,277,223; 4,194,529; 5,178,187; and applicant's earlier U.S. Pat. Nos. 4,962,290 and 5,273,822. Of the above related patents, only the '290, '223 and '822 patents provide an electrical signal along with the visual indication to advise personnel of the operational state of a valve to which the valve position indicator is attached.
Glockner et al. in U.S. Pat. No. 5,277,223 describes a valve position transmitter which provides both visual and electrical outputs indicative of valve position. The '223 indicator is comprised of a base, an adjusting ring, an indicator assembly, a transparent cover, switches, and cams for detecting rotation. The switches are actuated by a camming system, which are positionaly mounted on sliding splines. The position of the camming system must be adjusted, to effectively actuate the switch. This adjustment increases the amount of set-up time and further increases the complexity of the valve position indicator. Therefore, a need exist for a simple and economical valve position indicator which provides both visual and electrical outputs indicative of valve position. Also, a need exists for a valve position indicator that requires fewer elements, while indicating both visually and through an electrical output, the position of the valve.
It is also apparent from an examination of the above prior art patents that the means for attaching the indicator to the valve body varies considerably and does not follow any particular interface standard. For example, J. G. Pecis, in U.S. Pat. No. 3,238,968, shows an indicator attached to the valve body using one bolt. Sinclair et al., in both the above-mentioned '565 and '566 patents, shows a mounting ring portion of the indicator having three orifices for securing the indicator to the valve body. Raymond Jr., et al., in U.S. Pat. No. 5,178,187 shows a mounting pedestal having four bores symetrically positioned defining a square. The significance of the location of the bores is not at all clear from the disclosure.
In 1991, the Society of German Engineers and the Association of German Electrotechnicians, following the recommendations of the Standards Working Group for Instrumentation and Controls (NAMUR), promulgated a standard "VDI/VDE 3845" which defines the interfaces between rotary actuators, the fluid control valve bodies, and other accessories. VDI/VDE 3845 standardizes the height of the top mounted accessory, the position of the mounting bores, and the slot formed in the top of the actuator shaft. Thus, it is now advantageous, if not necessary for commercial marketing reasons, that valve position indicators meet these applicable international standards.
While the above prior art devices. could conceivably be jury-rigged to mate with the screw hole pattern defined by the NAMUR standard, it would be advantageous to have a valve position indicator especially designed to meet this standard so that no special adapters, mounting brackets, etc. would be required.
The present invention overcomes these and other disadvantages by providing an efficient to use and economical valve position indicator conforming with NAMUR standards. The valve position indicator provides both visual and electrical outputs indicative of valve position.